Rebekah Brooks and Andy Coulson have been branded "the scum of journalism" in a series of allegations from a former News of the World deputy features editor at the UK inquiry into press standards.

Paul McMullan accused Coulson of introducing "wholesale" phone hacking when he appointed editor of the News of the World in 2003, and described Brooks as "the criminal-in-chief".

In a dramatic two-hour testimony before the Leveson inquiry in London on Tuesday, McMullan made allegations about a "culture of illegality" that stretched from "the little men, the reporters" to senior police officers and politicians.

Lord Justice Leveson at times had to interject to warn McMullan that he risked incriminating himself while he was rattling off claims about alleged criminal wrongdoing during his time at News International's Sunday tabloid, which was closed at the height of the public outcry over phone hacking in July.

Asked whether his NoW editors knews that voicemail messages were being intercepted, McMullan said: "Yes ... I could go a bit further than that. We did all these things for our editors, for Rebekah Brooks and for Andy Coulson. You only have to read Coulson's column in Bizarre ... it was blatant and obvious. I don't think anyone realised that anyone was committing a crime at the start."

He added: "Andy Coulson brought that practice [phone hacking] wholesale with him when he was made deputy editor. They should have had the strength of conviction to say, 'Yes, sometimes you have to stray into black or grey illegal areas' ... instead they said we didn't know they were doing it. They should have been the heroes of journalism ... They're the scum of journalism for trying to drop me and my colleagues in it."

He later said: "For 21 years you have a culture of illegality of phone hacking and fiddling your expenses and so on. What you have is a future prime minister cosying up and being moulded by the arch-criminal, Rebekah Brooks, the criminal-in-chief."

Coulson and Brooks have separately and repeatedly denied any involvement or knowledge of criminal activity at the News of the World.

McMullan separately launched an extraordinary defence of paparazzi photographers, who have been criticised by alleged victims of intrusion who have given evidence to the inquiry over the past week.

"I absolutely loved giving chase to celebrities," he said. "Before [Princess] Diana died it was such good fun. How many jobs can you have car chases in? It was great."

He later claimed that "privacy is for paedos". "In 21 years of invading people's privacy I've never actually come across anyone who's been doing any good. Privacy is the space bad people need to do bad things in. Privacy is for paedos. If there is a privacy law your secrets are going to be much more valuable than they were before," McMullan said.

McMullan also defended his former colleagues on the now-closed NoW, saying they were "honest [and] honourable" journalists.

He said that hacking into murdered schoolgirl Milly Dowler's phone was "not a bad thing for a well-meaning journalist to do", claiming that they were trying to find the schoolgirl while she was still missing because they had such little faith in police to do the job.

• To contact the MediaGuardian news desk email editor@mediaguardian.co.uk or phone 020 3353 3857. For all other inquiries please call the main Guardian switchboard on 020 3353 2000. If you are writing a comment for publication, please mark clearly "for publication".

• To get the latest media news to your desktop or mobile, follow MediaGuardian on Twitter and Facebook